Substrate drying method and substrate processing apparatus

ABSTRACT

A substrate drying method includes a sublimation-agent-liquid-film placing step of placing a liquid film of a liquid sublimation agent on the front surface of the substrate, a high vapor-pressure liquid supply step of supplying a high vapor-pressure liquid that has vapor pressure higher than the sublimation agent and that does not include water to a rear surface that is a surface on a side opposite to the front surface in the substrate, a vaporizing/cooling step of, after the liquid film of the sublimation agent is placed on the front surface of the substrate, stopping supplying the high vapor-pressure liquid, and, as a result, losing vaporization heat in response to vaporization of the high vapor-pressure liquid, and, as a result, cooling the sublimation agent, and, as a result, solidifying the liquid film of the sublimation agent and a sublimating step of sublimating a sublimation-agent film.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to a substrate drying method and asubstrate processing apparatus. Examples of substrates to be processedinclude semiconductor wafers, substrates for liquid crystal displays,substrates for FPDs (Flat Panel Displays) such as organic EL(electroluminescence) displays, substrates for optical disks, substratesfor magnetic disks, substrates for magneto-optical disks, substrates forphotomasks, ceramic substrates, and substrates for solar cells.

2. Description of the Related Art

In a manufacturing process of a semiconductor device, a front surface ofa substrate, such as a semiconductor wafer, is processed with aprocessing liquid. A single-substrate processing type apparatus thatprocesses substrates one by one includes a spin chuck that rotates asubstrate while holding the substrate substantially horizontally and anozzle that supplies a processing liquid to a front surface of thesubstrate being rotated by the spin chuck.

In a typical substrate processing step, a chemical liquid is supplied toa substrate held by the spin chuck. Thereafter, a rinse liquid issupplied to the substrate, and, as a result, the chemical liquid on thesubstrate is replaced by the rinse liquid. Thereafter, a spin dry stepis performed to exclude the rinse liquid on the substrate. In the spindry step, the substrate is rotated at a high speed, and, as a result,the rinse liquid adhering to the substrate is shaken off and is removed(dried). A generally-used rinse liquid is deionized water.

A sublimation drying technique disclosed by Japanese Patent ApplicationPublication No. 2010-199261 has been proposed in order to restrain orprevent the occurrence of a pattern collapse in the spin dry step. InJapanese Patent Application Publication No. 2010-199261, a frozen filmis formed on a front surface of a substrate by supplying anultra-low-temperature nitrogen gas (about −60° C.) to the front surfaceof the substrate. An aqueous component included in the frozen film ofthe front surface of the substrate is sublimated by continuing to supplythe ultra-low-temperature nitrogen gas after the formation of the frozenfilm, and, as a result, the front surface of the substrate is driedwithout generating a liquid phase on the front surface of the substrate.

SUMMARY OF THE INVENTION

In the technique of Japanese Patent Application Publication No.2010-199261, an ultra-low-temperature nitrogen gas (about −60° C.) isrequired to be continuously supplied to the substrate, and thereforeequipment for supplying the nitrogen gas is needed, and there is a fearthat running costs will become enormous.

The present inventors have considered that a solvent that has asublimation capability and a low freezing point (as an example, afluorine-based organic solvent that has a ring structure (freezing pointof about 20.5° C.), tertiary butyl alcohol (freezing point of about 25°C.), or the like) is used as a sublimation agent, and have consideredthat a sublimation agent that is any one of these liquid sublimationagents is supplied to the front surface of the substrate, and haveconsidered that a liquid having a temperature lower than the freezingpoint of the sublimation agent is supplied to a rear surface of thesubstrate as a temperature-controlling fluid for solidifying (freezing)a solvent of a sublimation agent. In detail, the present inventorssupply cold water that has a liquid temperature of about 5° C. to about15° C. to the rear surface of the substrate as a temperature-controllingliquid. Thereafter, a sublimation agent is cooled by supplying the coldwater to the rear surface of the substrate, and as a result, thesublimation agent, such as a fluorine-based organic solvent having aring structure or tertiary butyl alcohol, is solidified, and asublimation-agent film is formed on the front surface of the substrate.Thereafter, the front surface of the substrate is dried by sublimatingthe sublimation-agent film.

However, in this technique, there is a fear that a water mist that hasoccurred in the rear surface of the substrate will flow around towardthe front-surface side of the substrate, and water will mix with thesublimation-agent film that has been solidified. If water has mixed withthe sublimation-agent film, there is a fear that the sublimation of thesublimation agent will be obstructed. Not only that, there is anotherfear that the pattern collapse will be promoted by the fact that wateris liquefied in the surface of the substrate. That is, it is required toprevent contamination of water into the sublimation-agent film that hasbeen solidified. Therefore, a solid sublimation-agent film has beendesired to be excellently formed while preventing contamination of waterinto the solid sublimation-agent film.

Therefore, it is an object of the present invention to provide asubstrate drying method and a substrate processing apparatus both ofwhich are capable of excellently forming a solid sublimation-agent filmwhile preventing contamination of water into the solid sublimation-agentfilm and hence capable of excellently realizing sublimation drying.

The present invention provides a substrate drying method including asublimation-agent-liquid-film placing step of placing a liquid film of aliquid sublimation agent on the front surface of the substrate, a highvapor-pressure liquid supply step of supplying a high vapor-pressureliquid that has vapor pressure higher than the sublimation agent andthat does not include water to a rear surface that is a surface on aside opposite to the front surface in the substrate, avaporizing/cooling step of, after the liquid film of the sublimationagent is placed on the front surface of the substrate, stoppingsupplying the high vapor-pressure liquid, and, as a result, losingvaporization heat in response to vaporization of the high vapor-pressureliquid, and, as a result, cooling the sublimation agent, and, as aresult, solidifying the liquid film of the sublimation agent, and, as aresult, forming a sublimation-agent film on the front surface of thesubstrate, and a sublimating step of sublimating the sublimation-agentfilm.

According to this method, a liquid film of a sublimation agent (i.e.,sublimation-agent liquid film) is placed on the front surface of thesubstrate. Furthermore, a high vapor-pressure liquid that has vaporpressure higher than the sublimation agent and that does not includewater is supplied to the rear surface of the substrate. After thesublimation-agent liquid film is placed on the front surface of thesubstrate, the supply of the high vapor-pressure liquid is stopped. As aresult, vaporization heat is lost from the substrate in response tovaporization of the high vapor-pressure liquid, and, as a result, asublimation agent included in the sublimation-agent liquid film iscooled, and, as a result, the sublimation-agent liquid film issolidified. As a result, it is possible to excellently form a solidsublimation-agent film while preventing contamination of water into thesolid sublimation-agent film.

Also, in the sublimating step, sublimating heat is lost in response tothe sublimation of the sublimation-agent film, and the sublimation-agentfilm is kept at or below a freezing point (melting point). Therefore, itis possible to prevent the sublimation agent included in thesublimation-agent film from being melted. This makes it possible toexcellently realize sublimation drying.

Also, the high vapor-pressure liquid does not include water, andtherefore it is possible to supply the high vapor-pressure liquid to thewhole area of the rear surface of the substrate without depending onwhether the rear surface of the substrate presents hydrophobicity. Thismakes it possible to perform vaporizing and cooling in the whole area ofthe substrate, and hence makes it possible to evenly cool thesublimation agent in the plane of the substrate. This makes it possibleto excellently solidify a sublimation agent included in thesublimation-agent liquid film.

In one preferred embodiment of the present invention, the highvapor-pressure liquid supplied to the rear surface of the substrate hasa liquid temperature higher than the freezing point of the sublimationagent.

According to this method, the high vapor-pressure liquid supplied to therear surface of the substrate has a liquid temperature higher than thefreezing point of the sublimation agent. Therefore, the sublimationagent on the front surface of the substrate is not immediately cooled toor below the freezing point of the sublimation agent by the supply ofthe high vapor-pressure liquid to the substrate. Therefore, it is alsopossible to perform the disposition of a sublimation-agent liquid filmon the front surface of the substrate and the supply of a highvapor-pressure liquid to the substrate in parallel with each other, andthis also makes it possible to shorten the period of time of the entireprocessing.

Also, it is possible to use a high vapor-pressure liquid at acomparatively high liquid temperature. It is also possible to use thehigh vapor-pressure liquid at a room temperature depending on the kindof the high vapor-pressure liquid (for example, in a case in which afluorine-based organic solvent whose freezing point is about 20.5° C.and that has a ring structure is employed as a sublimation agent). Inthis case, it is also possible to disuse a temperature control unit forhigh vapor-pressure liquids, and hence possible to reduce costs.

In one preferred embodiment of the present invention, thesublimation-agent-liquid-film placing step includes a sublimation-agentsupply step of supplying a sublimation agent to the front surface of thesubstrate and a thinning step of, on the front surface of the substrate,thinning the sublimation agent supplied to the front surface of thesubstrate by rotating the substrate around a predetermined rotationalaxis without supplying a sublimation agent.

According to this method, it is possible to spread the sublimation agentby a centrifugal force generated by the rotation of the substrate on thefront surface of the substrate. Consequently, it is possible toexcellently form a sublimation agent that has an appropriate and smallthickness on the front surface of the substrate, and it is possible toequalize the thickness of a sublimation-agent liquid film in the planeof the substrate.

In one preferred embodiment of the present invention, the highvapor-pressure liquid supply step is performed in parallel with thethinning step.

According to this method, the enlargement of the sublimation agent andthe supply of a high vapor-pressure liquid to the substrate areperformed in parallel with each other, and it is possible to shorten theperiod of time of the entire processing.

In one preferred embodiment of the present invention, the aforementionedmethod further includes a high-temperature liquid supply step ofsupplying a high-temperature liquid having a liquid temperature higherthan a freezing point of a sublimation agent to the rear surface of thesubstrate in parallel with the sublimation-agent-liquid-film placingstep.

According to this method, a high-temperature liquid having a liquidtemperature higher than a freezing point of a sublimation agent issupplied to the rear surface of the substrate in parallel with theplacement of the sublimation-agent liquid film on the front surface ofthe substrate. Therefore, it is possible to warm a sublimation agentsupplied to the front surface of the substrate, and hence possible toprevent the sublimation agent from being immediately solidified.Therefore, it is possible to form an excellent sublimation-agent liquidfilm on the front surface of the substrate.

In one preferred embodiment of the present invention, thehigh-temperature liquid includes the high vapor-pressure liquid.

According to this method, it is possible to warm a sublimation agentsupplied to the front surface of the substrate while more reliablypreventing water from mixing with the sublimation-agent liquid film onthe front surface of the substrate.

In one preferred embodiment of the present invention, thehigh-temperature liquid includes water.

According to this method, water is used as a high-temperature liquid,and therefore it is possible to make costs lower than in a case in whicha high vapor-pressure liquid is used as a high-temperature liquid.

In one preferred embodiment of the present invention, the aforementionedmethod further includes a substrate rotating step of rotating thesubstrate around a predetermined rotational axis in parallel with atleast either one of the sublimation-agent-liquid-film placing step andthe vaporizing/cooling step and a high-speed rotation step of rotatingthe substrate around the predetermined rotational axis at a speed higherthan in the substrate rotating step in parallel with the sublimatingstep.

According to this method, the substrate is rotated at a high speed inthe sublimating step. The contact speed between the sublimation-agentfilm and its circumambient atmosphere is increased by the high-speedrotation of the substrate. This makes it possible to advance thesublimation of the sublimation-agent film, and hence makes it possibleto sublimate the sublimation-agent film in a short time.

The present invention provides a substrate processing apparatusincluding a substrate holding unit that holds a substrate whose frontsurface has a pattern, a rotation unit that rotates a substrate held bythe substrate holding unit around a predetermined rotational axis, asublimation-agent supply unit that supplies a liquid sublimation agentto the front surface of the substrate, and a high vapor-pressure liquidsupply unit that supplies a high vapor-pressure liquid that has vaporpressure higher than the sublimation agent and that does not includewater to a rear surface that is a surface on a side opposite to thefront surface in the substrate.

According to this arrangement, a sublimation agent is supplied to thefront surface of the substrate. Consequently, a sublimation-agent liquidfilm is formed on the front surface of the substrate. Furthermore, ahigh vapor-pressure liquid that has vapor pressure higher than thesublimation agent and that does not include water is supplied to therear surface of the substrate.

After the sublimation-agent liquid film is placed on the front surfaceof the substrate, the supply of the high vapor-pressure liquid isstopped. As a result, vaporization heat is lost from the substrate inresponse to vaporization of the high vapor-pressure liquid, and, as aresult, a sublimation agent included in the sublimation-agent liquidfilm is cooled, and, as a result, the sublimation-agent liquid film issolidified. As a result, it is possible to excellently form a solidsublimation-agent film while preventing contamination of water into thesolid sublimation-agent film. This makes it possible to excellentlysolidify the sublimation agent included in the sublimation-agent liquidfilm.

In one preferred embodiment of the present invention, the highvapor-pressure liquid supplied to the rear surface of the substrate hasa liquid temperature higher than a freezing point of a sublimationagent.

According to this arrangement, the high vapor-pressure liquid suppliedto the rear surface of the substrate has a liquid temperature higherthan the freezing point of the sublimation agent. Therefore, thesublimation agent on the front surface of the substrate is notimmediately cooled to or below the freezing point of the sublimationagent by the supply of the high vapor-pressure liquid to the substrate.Therefore, it is also possible to perform the disposition of asublimation-agent liquid film on the front surface of the substrate andthe supply of a high vapor-pressure liquid to the substrate in parallelwith each other, and this also makes it possible to shorten the periodof time of the entire processing.

Also, it is possible to use a high vapor-pressure liquid at acomparatively high liquid temperature. It is also possible to use thehigh vapor-pressure liquid at a room temperature depending on the kindof the high vapor-pressure liquid (for example, in a case in which afluorine-based organic solvent whose freezing point is about 20.5° C.and that has a ring structure is employed as a sublimation agent). Inthis case, it is also possible to disuse a temperature control unit forhigh vapor-pressure liquids, and hence possible to reduce costs.

In one preferred embodiment of the present invention, the substrateprocessing apparatus further includes a controller that controls therotation unit, the sublimation-agent supply unit, and the highvapor-pressure liquid supply unit. The controller may execute asublimation-agent-liquid-film placing step of placing a liquid film ofthe sublimation agent on the front surface of the substrate by means ofthe rotation unit and the sublimation-agent supply unit, a highvapor-pressure liquid supply step of supplying a high vapor-pressureliquid to the rear surface of the substrate by means of the highvapor-pressure liquid supply unit, a vaporizing/cooling step of, afterthe liquid film of the sublimation agent is placed on the front surfaceof the substrate, stopping supplying the high vapor-pressure liquid,and, as a result, losing vaporization heat in response to vaporizationof the high vapor-pressure liquid, and, as a result, cooling thesublimation agent, and, as a result, solidifying the liquid film of thesublimation agent, and, as a result, forming a sublimation-agent film onthe front surface of the substrate, and a sublimating step ofsublimating the sublimation-agent film by means of the rotation unit.

According to this arrangement, a liquid film of a sublimation agent isplaced on the front surface of the substrate. Furthermore, a highvapor-pressure liquid that has vapor pressure higher than thesublimation agent and that does not include water is supplied to therear surface of the substrate. After the sublimation-agent liquid filmis placed on the front surface of the substrate, the supply of the highvapor-pressure liquid is stopped. As a result, vaporization heat is lostfrom the substrate in response to vaporization of the highvapor-pressure liquid, and, as a result, a sublimation agent included inthe sublimation-agent liquid film is cooled, and, as a result, thesublimation-agent liquid film is solidified. As a result, it is possibleto excellently form a solid sublimation-agent film while preventingcontamination of water into the solid sublimation-agent film.

Also, in the sublimating step, sublimating heat is lost in response tothe sublimation of the sublimation-agent film, and the sublimation-agentfilm is kept at or below a freezing point (melting point). Therefore, itis possible to prevent the sublimation agent included in thesublimation-agent film from being melted. This makes it possible toexcellently realize sublimation drying.

Also, the high vapor-pressure liquid does not include water, andtherefore it is possible to supply the high vapor-pressure liquid to thewhole area of the rear surface of the substrate without depending onwhether the rear surface of the substrate presents hydrophobicity. Thismakes it possible to perform vaporizing and cooling in the whole area ofthe substrate, and hence makes it possible to evenly cool thesublimation agent in the plane of the substrate. This makes it possibleto excellently solidify a sublimation agent included in thesublimation-agent liquid film.

In one preferred embodiment of the present invention, the controllerexecutes a sublimation-agent supply step of supplying a sublimationagent to the front surface of the substrate by means of thesublimation-agent supply unit in the sublimation-agent-liquid-filmplacing step and a thinning step of, on the front surface of thesubstrate, thinning the sublimation agent supplied to the front surfaceof the substrate by rotating the substrate around a predeterminedrotational axis without supplying a sublimation agent by means of therotation unit in the sublimation-agent-liquid-film placing step.

According to this arrangement, it is possible to spread the sublimationagent by a centrifugal force generated by the rotation of the substrateon the front surface of the substrate. Consequently, it is possible toexcellently form a sublimation agent that has an appropriate and smallthickness on the front surface of the substrate, and it is possible toequalize the thickness of a sublimation-agent liquid film in the planeof the substrate.

In one preferred embodiment of the present invention, the controllerexecutes the high vapor-pressure liquid supply step in parallel with thethinning step.

According to this arrangement, the enlargement of the sublimation agentand the supply of a high vapor-pressure liquid to the substrate areperformed in parallel with each other, and therefore it is possible toshorten the period of time of the entire processing.

In one preferred embodiment of the present invention, the substrateprocessing apparatus further includes a high-temperature liquid supplyunit that supplies a high-temperature liquid having a liquid temperaturehigher than a freezing point of a sublimation agent to the rear surfaceof the substrate. The controller may further execute a high-temperatureliquid supply step of supplying a high-temperature liquid having aliquid temperature higher than a freezing point of a sublimation agentto the rear surface of the substrate by means of the high-temperatureliquid supply unit in parallel with the sublimation-agent-liquid-filmplacing step.

According to this arrangement, a high-temperature liquid having a liquidtemperature higher than a freezing point of a sublimation agent issupplied to the rear surface of the substrate in parallel with thesupply of a sublimation agent to the front surface of the substrate.Therefore, it is possible to warm a sublimation agent supplied to thefront surface of the substrate, and hence possible to prevent thesublimation agent from being immediately solidified. Therefore, it ispossible to form an excellent sublimation-agent liquid film on the frontsurface of the substrate.

In one preferred embodiment of the present invention, thehigh-temperature liquid includes the high vapor-pressure liquid.

According to this arrangement, it is possible to warm a sublimationagent supplied to the front surface of the substrate while more reliablypreventing water from mixing with the sublimation-agent liquid film onthe front surface of the substrate.

In one preferred embodiment of the present invention, thehigh-temperature liquid includes water.

According to this arrangement, water is used as a high-temperatureliquid, and therefore it is possible to make costs lower than in a casein which a high vapor-pressure liquid is used as a high-temperatureliquid.

In one preferred embodiment of the present invention, the controllerfurther executes a substrate rotating step of rotating the substratearound a predetermined rotational axis in parallel with at least eitherone of the sublimation-agent-liquid-film placing step and thevaporizing/cooling step and a high-speed rotation step of rotating thesubstrate around the predetermined rotational axis at a speed higherthan in the substrate rotating step in parallel with the sublimatingstep.

According to this arrangement, the substrate is rotated at a high speedin the sublimating step. The contact speed between the sublimation-agentfilm and its circumambient atmosphere is increased by the high-speedrotation of the substrate. This makes it possible to advance thesublimation of the sublimation-agent film, and hence makes it possibleto sublimate the sublimation-agent film in a short time.

The aforementioned or other objects, features, and effects of thepresent invention will be clarified by the following description ofpreferred embodiments given below with reference to the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of a substrate processing apparatus, which isseen from above, according to a preferred embodiment of the presentinvention.

FIG. 2 is an illustrative cross-sectional view shown to describe anarrangement example of a processing unit included in the substrateprocessing apparatus.

FIG. 3 is a block diagram shown to describe an electrical configurationof a main part of the substrate processing apparatus.

FIG. 4 is an enlarged cross-sectional view of a front surface of asubstrate that is to be processed by the substrate processing apparatus.

FIG. 5 is a flowchart shown to describe the contents of a firstsubstrate processing example performed in the processing unit.

FIG. 6 is a flowchart shown to describe a sublimation drying step ofFIG. 5.

FIG. 7A to FIG. 7D are schematic views, each showing a state around thesubstrate when the sublimation drying step is performed.

FIG. 8A and FIG. 8B are schematic views shown to describe asublimation-agent supply step according to a second substrate processingexample and a sublimation-agent supply step according to a thirdsubstrate processing example, respectively.

FIG. 9 shows a modification of the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1 is a schematic view of a substrate processing apparatus 1, whichis seen from above, according to a preferred embodiment of the presentinvention. The substrate processing apparatus 1 is a single-substrateprocessing type apparatus that processes substrates W, such as siliconwafers, one by one. In the present preferred embodiment, the substrate Wis a disk-shaped substrate. The substrate processing apparatus 1includes a plurality of processing units 2 each of which processes asubstrate W by use of a processing liquid and a rinse liquid, a loadport LP at which a substrate container C that contains each of aplurality of substrates W that are processed by the processing units 2is placed, an indexer robot IR and a substrate transfer robot CR each ofwhich transfers a substrate W between the load port LP and theprocessing unit 2, and a controller 3 that controls the substrateprocessing apparatus 1. The indexer robot IR transfers the substrate Wbetween the substrate container C and the substrate transfer robot CR.The substrate transfer robot CR transfers the substrate W between theindexer robot IR and the processing unit 2. The plurality of processingunits 2 are identical, for example, in configuration with each other.

FIG. 2 is an illustrative cross-sectional view shown to describe anarrangement example of the processing unit 2.

The processing unit 2 includes a box-shaped chamber 4, a spin chuck(substrate holding unit) 5 that rotates a substrate W around a verticalrotational axis A1 passing through the center of the substrate W whileholding the single substrate W in a horizontal attitude in the chamber4, a sublimation-agent supply unit that supplies a liquid sublimationagent to an upper surface of the substrate W (a front surface Wa of thesubstrate W (see FIG. 4 and the like)) held by the spin chuck 5, a highvapor-pressure liquid supply unit that supplies IPA (isopropyl alcohol),which is an example of a high vapor-pressure liquid that has vaporpressure higher than water (i.e., vapor pressure higher than thesublimation agent) and that does not include water, to a lower surfaceof the substrate W (a rear surface Wb of the substrate W) held by thespin chuck 5, a shielding member 6 that faces the upper surface of thesubstrate W held by the spin chuck 5 and that blocks a space existingabove the substrate W from its circumambient atmosphere, a lower-surfacenozzle 7 that discharges a processing liquid toward a central part ofthe lower surface of the substrate W (the rear surface Wb of thesubstrate W (see FIG. 7A and the like)) held by the spin chuck 5, and acylindrical processing cup 8 that surrounds the lateral side of the spinchuck 5.

The chamber 4 includes a box-shaped partition wall 11 that contains thespin chuck 5, etc.

A clamping-type chuck that clamps the substrate W in a horizontaldirection and that horizontally holds the substrate W is employed as thespin chuck 5. In detail, the spin chuck 5 includes a spin motor(rotation unit) 12, a lower spin shaft 13 that is integrally united witha driving shaft of the spin motor 12, and a disk-shaped spin base 14that is substantially horizontally attached to an upper end of the lowerspin shaft 13.

The spin base 14 includes a horizontal and circular upper surface 14 athat has an outer diameter greater than that of the substrate W. Aplurality of (three or more, e.g., six) clamping members 15 are disposedon the upper surface 14 a at its peripheral edge. The clamping members15 are spaced out with suitable intervals there between, e.g., arespaced out evenly on a circumference corresponding to the outerperipheral shape of the substrate W at the peripheral edge of the uppersurface of the spin base 14.

The shielding member 6 includes a shielding plate 17, an upper spinshaft 18 that is disposed at the shielding plate 17 so as to berotatable together with the shielding plate 17, and an upper-surfacenozzle 19 that passes through a central part of the shielding plate 17in an up-down direction. The shielding plate 17 includes a disk portion20 that is horizontally disposed and a cylindrical portion 21 that isdisposed along an outer peripheral edge of the disk portion 20. The diskportion 20 is formed in a disk shape whose diameter is substantiallyequal to or greater than that of the substrate W. The disk portion 20has its lower surface having a circular substrate-facing surface 20 athat faces the whole area of the upper surface of the substrate W. Acylindrical through hole 20 b that upwardly and downwardly passesthrough the disk portion 20 is formed in a central part of thesubstrate-facing surface 20 a. The through hole 20 b is defined by acylindrical inner peripheral surface.

The cylindrical portion 21 may be formed in a truncated cone shape. Thecylindrical portion 21 may extend downwardly so as to spread outwardlyfrom the outer peripheral edge of the disk portion 20 as shown in FIG.2. Also, the cylindrical portion 21 may become smaller in thickness inproportion to an approach to a lower end of the cylindrical portion 21as shown in FIG. 2.

The upper spin shaft 18 is disposed rotatably around a rotational axisA2 (an axis that coincides with the rotational axis A1 of the substrateW) that passes through the center of the shielding plate 17 and thatextends vertically. The upper spin shaft 18 is circularly cylindrical.An inner peripheral surface of the upper spin shaft 18 is formed at acylindrical plane that centers on the rotational axis A2. An internalspace of the upper spin shaft 18 communicates with the through hole 20 bof the shielding plate 17. The upper spin shaft 18 is relativelyrotatably supported by a support arm 22 that horizontally extends abovethe shielding plate 17.

In the present preferred embodiment, the upper-surface nozzle 19functions as a center shaft nozzle. The upper-surface nozzle 19 isdisposed above the spin chuck 5. The upper-surface nozzle 19 issupported by the support arm 22. The upper-surface nozzle 19 isunrotatable with respect to the support arm 22. The upper-surface nozzle19 moves up and down together with the shielding plate 17, the upperspin shaft 18, and the support arm 22. The upper-surface nozzle 19 hasits lower end in which a discharge port 19 a that faces a central partof the upper surface of the substrate W held by the spin chuck 5 isformed.

A shielding-plate rotation unit 26 configured to include an electricmotor and the like is joined to the shielding plate 17. Theshielding-plate rotation unit 26 rotates the shielding plate 17 and theupper spin shaft 18 around the rotational axis A2 with respect to thesupport arm 22. A shielding-member lifting unit 27 configured to includean electric motor, a ball screw, etc., is joined to the support arm 22.The shielding-member lifting unit 27 raises and lowers the shieldingmember 6 (the shielding plate 17 and the upper spin shaft 18) and theupper-surface nozzle 19 together with the support arm 22 in a verticaldirection.

The shielding-member lifting unit 27 raises and lowers the shieldingplate 17 between a shielding position at which the substrate-facingsurface 20 a approaches the upper surface of the substrate W held by thespin chuck 5 and at which the height of the lower end of the cylindricalportion 21 is placed below the height of the substrate W (shown by thealternate long and two short dashed line in FIG. 2. See also FIG. 7A andthe like) and a retreat position that retreats greatly more upwardlythan the shielding position (shown by the solid line in FIG. 2). Theshielding-member lifting unit 27 is capable of holding the shieldingplate 17 at the shielding position, at a nearby position (shown by thebroken line in FIG. 2), and at the retreat position. The shieldingposition is a position at which the substrate-facing surface 20 a formsa shielding space 28 (see FIG. 7B and the like) between the uppersurface of the substrate W and the substrate-facing surface 20 a.Although the shielding space 28 is not completely isolated from itscircumambient space, a gas does not flow into the shielding space 28from the circumambient space. In other words, the shielding space 28 issubstantially shielded from its circumambient space. The nearby positionis placed slightly above the retreat position. In a state in which theshielding plate 17 is placed at the nearby position, a space between thesubstrate-facing surface 20 a of the shielding plate 17 and thesubstrate W is not shielded from the circumambient space.

The sublimation-agent supply unit includes the upper-surface nozzle 19and a sublimation agent unit 31 that supplies a liquid sublimation agentto the upper-surface nozzle 19. The sublimation agent unit 31 includes asublimation agent pipe 32 connected to the upper-surface nozzle 19 and asublimation agent valve 33 interposed in the sublimation agent pipe 32.The sublimation agent supplied to the sublimation agent pipe 32 is asolvent that has a sublimation capability and whose freezing point islow, and a solvent such as a fluorine-based organic solvent having aring structure (whose freezing point is about 20.5° C.) or tertiarybutyl alcohol (whose freezing point is about 25° C.) can be mentioned asan example. The sublimation agent supplied to the sublimation agent pipe32 is a liquid sublimation agent whose temperature is slightly higherthan the freezing point. In a case in which a fluorine-based organicsolvent having a ring structure is employed as a sublimation agent, asublimation agent having a room temperature (about 23° C. to about 25°C.) is given to the sublimation agent pipe 32. In a case in whichtertiary butyl alcohol is employed as a sublimation agent, a sublimationagent that has undergone temperature control so as to have a temperatureof about 30° C. is given to the sublimation agent pipe 32. A liquidsublimation agent is supplied to the upper-surface nozzle 19 by openingthe sublimation agent valve 33, and, as a result, the liquid sublimationagent is discharged downwardly from the discharge port 19 a. The use ofa fluorine-based organic solvent having a ring structure as asublimation agent also makes it possible to disuse a temperature controlunit for high vapor-pressure liquids, and it is possible to use thesublimation agent at a room temperature, and therefore it is possible toreduce costs.

An acid chemical-liquid supply unit 34, an alkaline chemical-liquidsupply unit 35, a rinse-liquid supply unit 36, an organic-solvent supplyunit 37, and a gas supply unit 38 are connected to the upper-surfacenozzle 19.

The acid chemical-liquid supply unit 34 includes an acid chemical-liquidpipe 41 connected to the upper-surface nozzle 19 and an acidchemical-liquid valve 42 interposed in the acid chemical-liquid pipe 41.A chemical liquid including at least one of a group consisting of, forexample, hydrofluoric acid (HF), hydrochloric acid, sulfuric acid,phosphoric acid, and nitric acid can be mentioned as an acid chemicalliquid given to the acid chemical-liquid pipe 41. In the presentpreferred embodiment, hydrofluoric acid (HF) is employed as an acidchemical liquid. An acid chemical liquid is supplied to theupper-surface nozzle 19 by opening the acid chemical-liquid valve 42,and, as a result, the acid chemical liquid is discharged downwardly fromthe discharge port 19 a.

The alkaline chemical-liquid supply unit 35 includes an alkalinechemical-liquid pipe 43 connected to the upper-surface nozzle 19 and analkaline chemical-liquid valve 44 interposed in the alkalinechemical-liquid pipe 43. A chemical liquid including at least one of agroup consisting of, for example, ammonia and hydroxyl can be mentionedas an alkaline chemical liquid given to the alkaline chemical-liquidpipe 43. In the present preferred embodiment, SC1 (a liquid thatincludes NH₄OH and H₂O₂) is employed as an alkaline chemical liquid. Analkaline chemical liquid is supplied to the upper-surface nozzle 19 byopening the alkaline chemical-liquid valve 44, and, as a result, thealkaline chemical liquid is discharged downwardly from the dischargeport 19 a.

The rinse-liquid supply unit 36 includes a rinse liquid pipe 45connected to the upper-surface nozzle 19 and a rinse liquid valve 46interposed in the rinse liquid pipe 45. A rinse liquid given to therinse liquid pipe 45 is, for example, deionized water (DIW), and yet,without being limited to DIW, the rinse liquid may be any one ofcarbonated water, electrolyzed ion water, hydrogen water, ozone water,and hydrochloric acid water having a diluted concentration (for example,about 10 ppm to 100 ppm). A rinse liquid is supplied to theupper-surface nozzle 19 by opening the rinse liquid valve 46, and, as aresult, the rinse liquid is discharged downwardly from the dischargeport 19 a.

The organic-solvent supply unit 37 is a unit for supplying an organicsolvent serving as a low-surface-tension liquid that is larger inspecific gravity than air and that has surface tension lower than water.The organic-solvent supply unit 37 includes an organic solvent pipe 47connected to the upper-surface nozzle 19 and an organic solvent valve 48interposed in the organic solvent pipe 47. The organic solvent given tothe organic solvent pipe 47 is, for example, IPA (isopropyl alcohol),and, for example, methanol, ethanol, acetone, EG (ethylene glycol), andHFE (hydrofluoroether) can be mentioned as the organic solvent, besidesIPA. Also, a liquid mixed with other components may be used as theorganic solvent without being limited to a monocomponent liquid. Theorganic solvent may be, for example, a mixed liquid of IPA and acetone,or may be, for example, a mixed liquid of IPA and methanol.

The gas supply unit 38 includes a gas supply pipe 49 connected to theupper-surface nozzle 19 and a gas valve 50 that opens and closes the gassupply pipe 49. The gas given to the gas supply pipe 49 is adehumidified gas, particularly, a dehumidified inert gas. The inert gasincludes, for example, a nitrogen gas and an argon gas. The gas issupplied to the upper-surface nozzle 19 by opening the gas valve 50,and, as a result, the gas is discharged downwardly from the dischargeport 19 a.

The high vapor-pressure liquid supply unit includes the lower-surfacenozzle 7 and a high vapor-pressure liquid unit 51 that supplies IPA(isopropyl alcohol), which is an example of a high vapor-pressureliquid, to the lower-surface nozzle 7.

The lower-surface nozzle 7 has a single discharge port 7 a facing thecentral part of the lower surface of the substrate W held by the spinchuck 5. The discharge port 7 a discharges a liquid vertically upwardly.The liquid discharged therefrom substantially perpendicularly strikesthe central part of the lower surface of the substrate W held by thespin chuck 5. A lower-surface supply pipe 52 is connected to thelower-surface nozzle 7. The lower-surface supply pipe 52 is insertedinto the inside of the lower spin shaft 13 that is a hollow shaft andthat is disposed vertically.

The high vapor-pressure liquid unit 51 includes a high vapor-pressureliquid pipe 53 connected to the lower-surface supply pipe 52 and a highvapor-pressure liquid valve 54 interposed in the high vapor-pressureliquid pipe 53. A high vapor-pressure liquid given to the highvapor-pressure liquid pipe 53 is a liquid that has vapor pressure higherthan water (vapor pressure higher than a sublimation agent) (i.e., thathas a boiling point lower than water) and that does not include water.The high vapor-pressure liquid is, for example, a solvent, and, morespecifically, is IPA (isopropyl alcohol). For example, methanol,ethanol, acetone, and HFE (hydrofluoroether) can be mentioned as thehigh vapor-pressure liquid (solvent), besides IPA. Also, a liquid mixedwith other components may be used as the high vapor-pressure liquidwithout being limited to a monocomponent liquid. The high vapor-pressureliquid may be, for example, a mixed liquid of IPA and acetone, or maybe, for example, a mixed liquid of IPA and methanol.

The temperature of the high vapor-pressure liquid supplied to the highvapor-pressure liquid pipe 53 is several degrees (° C.) higher than thefreezing point of the sublimation agent (solvent) supplied to thesublimation agent pipe 32. In a case in which a fluorine-based organicsolvent having a ring structure is employed as a sublimation agentsupplied to the sublimation agent pipe 32, the high vapor-pressureliquid has a room temperature, and is given to the lower-surface supplypipe 52. In a case in which tertiary butyl alcohol is employed as asublimation agent, the high vapor-pressure liquid has a temperature ofabout 30° C., and is given to the lower-surface supply pipe 52.

When the high vapor-pressure liquid valve 54 is opened, a highvapor-pressure liquid is supplied to the lower-surface nozzle 7 throughthe high vapor-pressure liquid pipe 53 and through the lower-surfacesupply pipe 52. The lower-surface nozzle 7 discharges the highvapor-pressure liquid supplied thereto substantially vertically upwardlyfrom the discharge port 7 a, and the high vapor-pressure liquiddischarged from the lower-surface nozzle 7 substantially perpendicularlystrikes the central part of the lower surface of the substrate W held bythe spin chuck 5.

The processing cup 8 is disposed at a more outward position than thesubstrate W held by the spin chuck 5 (in a direction away from therotational axis A1). The processing cup 8 includes a plurality of cups61 to 63 (first to third cups 61 to 63) surrounding the circumference ofthe spin base 14, a plurality of guards 64 to 66 (inner guard 64,intermediate guard 65, outer guard 66) each of which receives processingliquids (chemical liquid, rinse liquid, organic solvent, hydrophobizingagent, and the like) that have scattered around the substrate W, and aguard lifting unit 67 (see FIG. 5) that individually raises and lowersthe plurality of guards 64 to 66. The processing cup 8 is disposedoutside the outer periphery of the substrate W held by the spin chuck 5(in the direction away from the rotational axis A1).

Each cup 61 to 63 is circularly cylindrical, and surrounds the peripheryof the spin chuck 5. The second cup 62 that is the second from theinside is disposed outside the first cup 61, and the outermost third cup63 is disposed outside the second cup 62. The third cup 63 is, forexample, integrally united with the intermediate guard 65, and is raisedand lowered together with the intermediate guard 65. Each cup 61 to 63forms an annular groove that is upwardly opened.

A drainage pipe 76 is connected to the groove of the first cup 61. Aprocessing liquid guided to the groove of the first cup 61 is sent towaste-liquid equipment placed outside the apparatus through the drainagepipe 76.

A collection pipe 77 is connected to the groove of the second cup 62. Aprocessing liquid (chiefly, chemical liquid) guided to the groove of thesecond cup 62 is sent to the collection equipment placed outside theapparatus through the collection pipe 77, and is collected and processedin the collection equipment.

A collection pipe 78 is connected to the groove of the third cup 63. Aprocessing liquid (for example, organic solvent) guided to the groove ofthe third cup 63 is sent to the collection equipment placed outside theapparatus through the collection pipe 78, and is collected and processedin the collection equipment.

Each guard 64 to 66 is circularly cylindrical, and surrounds theperiphery of the spin chuck 5. Each guard 64 to 66 includes acylindrical guide portion 68 that surrounds the periphery of the spinchuck 5 and a cylindrical inclined portion 69 that extends obliquelyupwardly toward the center side from an upper end of the guide portion68 (in a direction approaching the rotational axis A1 of the substrateW). An upper end part of each inclined portion 69 defines an innerperipheral part of each guard 64 to 66, and has a diameter greater thanthe substrate W and than the spin base 14. The three inclined portions69 are piled together upwardly and downwardly, and the three guideportions 68 are disposed coaxially. The three guide portions 68 (guideportions 68 of the guards 64 to 66) are capable of coming into or out ofthe corresponding cups 61 to 63, respectively. In other words, theprocessing cup 8 is collapsible, and is folded and unfolded by allowingthe guard lifting unit 67 to raise and lower at least one of the threeguards 64 to 66. In the inclined portion 69, its sectional shape may belinear as shown in FIG. 2, or may extend, for example, smoothly whilemaking a convex circular arc.

Each guard 64 to 66 is raised and lowered between an upper position(where the upper end part of each inclined portion 69 is placed abovethe upper surface of the substrate W) and a lower position (where theupper end part of each inclined portion 69 is placed below the uppersurface of the substrate W) by driving the guard lifting unit 67.

In a state in which any one of the guards 64 to 66 faces a peripheralend surface of the substrate W, a processing liquid (acid chemicalliquid, alkaline chemical liquid, rinse liquid, organic solvent,sublimation agent, high vapor-pressure liquid, etc.) is supplied to thesubstrate W, or the substrate W is dried. In order to realize a state inwhich, for example, the outermost outer guard 66 faces the peripheralend surface of the substrate W (state of FIG. 7D, which is hereinafterreferred to as the “third guard facing state” when necessary), the innerguard 64 and the intermediate guard 65 are placed at the lower position,and the outer guard 66 is placed at the upper position. In the thirdguard facing state, all of the processing liquid discharged from theperipheral edge of the substrate W being in a rotational state isreceived by the outer guard 66.

In order to realize a state in which the intermediate guard 65, which isthe second from the inside, faces the peripheral end surface of thesubstrate W (state of FIG. 7A, etc., which is hereinafter referred to asthe “second guard facing state” when necessary), the inner guard 64 isplaced at the lower position, and the intermediate guard 65 and theouter guard 66 are placed at the upper position. In the second guardfacing state, all of the processing liquid discharged from theperipheral edge of the substrate W being in a rotational state isreceived by the intermediate guard 65.

In order to realize a state in which the innermost inner guard 64 facesthe peripheral end surface of the substrate W (not shown, which ishereinafter referred to as the “first guard facing state” whennecessary), all of the three guards 64 to 66 are placed at the upperposition. In the first guard facing state, all of the processing liquiddischarged from the peripheral edge of the substrate W being in arotational state is received by the inner guard 64.

For example, in a state in which any one of the three guards 64 to 66faces the peripheral end surface of the substrate W, a HF step S3 (seeFIG. 5), a rinse step S4 (see FIG. 5), an SC1 step S5 (see FIG. 5), arinse step S6 (see FIG. 5), a replacing step S7 (see FIG. 5), and asublimation drying step S8 (see FIG. 5), which are described later, areperformed. Therefore, a processing liquid that has scattered around thesubstrate W when a processing liquid is being supplied to the substrateW is guided to any one of the cups 61 to 63 by means of any one of theinner guard 64, the intermediate guard 65, and the outer guard 66.

FIG. 3 is a block diagram shown to describe an electrical configurationof a main part of the substrate processing apparatus 1.

The controller 3 is formed by use of, for example, a microcomputer. Thecontroller 3 has an arithmetic unit, such as CPU, a storage unit, suchas a read-only memory device and a hard disk drive, and an input-outputunit. A program executed by the arithmetic unit is stored in the storageunit.

The spin motor 12, the shielding-member lifting unit 27, theshielding-plate rotation unit 26, the guard lifting unit 67, etc., whichare to be controlled, are connected to the controller 3. The controller3 controls the operations of the spin motor 12, the shielding-memberlifting unit 27, the shielding-plate rotation unit 26, the guard liftingunit 67, etc., in accordance with a predetermined program.

Also, the controller 3 opens and closes the sublimation agent valve 33,the acid chemical-liquid valve 42, the alkaline chemical-liquid valve44, the rinse liquid valve 46, the organic solvent valve 48, the gasvalve 50, and the high vapor-pressure liquid valve 54 in accordance witha predetermined program.

A description will be hereinafter given of a case in which a substrate Whaving its front surface Wa that is a device-forming surface and onwhich a pattern 100 is formed is processed.

FIG. 4 is an enlarged cross-sectional view of a front surface Wa of asubstrate W that is to be processed by the substrate processingapparatus 1. The substrate W to be processed is, for example, a siliconwafer. A pattern 100 is formed on the front surface Wa that is a patternforming surface. The pattern 100 is, for example, a microscopic pattern.The pattern 100 may be a pattern in which structural elements 101 eachof which has a convex shape (pillar shape) are disposed in a matrixmanner as shown in FIG. 4. In this case, the pattern 100 is formed suchthat a line width W1 of the structural element 101 is, for example,about 3 nm to 45 nm and such that a gap W2 of the pattern 100 is, forexample, about 10 nm to several μm, respectively. A film thickness T ofthe pattern 100 is, for example, about 0.2 μm to 1.0 μm. Also, thepattern 100 may be formed such that, for example, an aspect ratio (ratioof the film thickness T with respect to the line width W1) is, forexample, about 5 to 500 (typically, it is about 5 to 50).

Also, the pattern 100 may be formed such that a linear pattern formed bya microscopic trench is repeatedly arranged. Also, the pattern 100 maybe formed such that a plurality of microscopic holes (voids or pores)are made in a thin film.

The pattern 100 includes, for example, an insulating film. The pattern100 may also include a conductor film. More specifically, the pattern100 may be formed with a laminated film in which a plurality of filmsare stacked together, and may include an insulating film and a conductorfilm. The pattern 100 may be a pattern made of a single layer film. Theinsulating film may be a silicon oxide film (SiO₂ film) or may be asilicon nitride film (SiN film). Also, the conductor film may be anamorphous silicon film doped with impurities for low resistivity, or maybe a metal film (for example, TiN film).

Also, the pattern 100 may be a hydrophilic film. A TEOS film (kind ofsilicon oxide film) can be mentioned as an example of the hydrophilicfilm.

FIG. 5 is a flowchart shown to describe the contents of a firstsubstrate processing example performed in the processing unit 2. Thefirst substrate processing example will be described with reference toFIG. 1 to FIG. 5.

An unprocessed substrate W (for example, a circular substrate having adiameter of 300 mm) is carried into the processing unit 2 from thesubstrate container C by means of the indexer robot IR and the substratetransfer robot CR, is then carried into the chamber 4, is then deliveredto the spin chuck 5 in a state in which the front surface Wa (see FIG. 4and the like) of the substrate W is directed upwardly, and is held bythe spin chuck 5 (S1 of FIG. 5: Carry-in of Substrate W). In this state,the rear surface Wb of the substrate W (see FIG. 7A and the like) isdirected downwardly. The substrate W is carried into the chamber 4 in astate in which the shielding plate 17 has been retreated to the retreatposition and in a state in which the guards 64 to 66 have been placed atthe lower position.

After the substrate transfer robot CR is retreated outwardly from theprocessing unit 2, the controller 3 increases the rotation speed of thespin base 14 to a predetermined liquid treatment speed (within the rangeof about 10 to 1200 rpm, e.g., about 300 rpm) while controlling the spinmotor 12, and maintains the liquid treatment speed (S2 of FIG. 5: Startof rotation of Substrate W).

Furthermore, the controller 3 lowers the shielding plate 17 from theretreat position, and places it at the nearby position while controllingthe shielding-member lifting unit 27.

Furthermore, the controller 3 allows the inner guard 64 to face theperipheral end surface of the substrate W (i.e., realizes a first guardfacing state) by raising the inner guard 64, the intermediate guard 65,and the outer guard 66 to the upper position while controlling the guardlifting unit 67.

When the rotation of the substrate W reaches the liquid treatment speed,the controller 3 then performs the HF step S3 (see FIG. 5) in which HF,which is an example of an acid chemical liquid, is supplied to the frontsurface Wa of the substrate W. In detail, the controller 3 opens theacid chemical-liquid valve 42. As a result, HF is discharged from thedischarge port 19 a of the upper-surface nozzle 19 toward the centralpart of the front surface Wa of the substrate W being in a rotationalstate. HF supplied to the front surface Wa of the substrate W moves tothe peripheral edge of the substrate W while receiving a centrifugalforce generated by the rotation of the substrate W. Consequently, thewhole area of the front surface Wa of the substrate W is processed byuse of HF.

HF that has moved to the peripheral edge of the substrate W isdischarged from the peripheral edge of the substrate W in a lateraldirection of the substrate W. HF discharged from the peripheral edge ofthe substrate W is received by an inner wall of the inner guard 64, isthen allowed to flow down along the inner wall of the inner guard 64,and is sent to waste liquid treatment equipment placed outside theapparatus through the first cup 61 and through the drainage pipe 76.

When a predetermined period of time elapses from the start of dischargeof HF, the controller 3 closes the acid chemical-liquid valve 42, andstops the discharge of HF from the upper-surface nozzle 19.Consequently, the HF step S3 is ended.

Thereafter, the controller 3 performs the rinse step S4 (see FIG. 5) inwhich a chemical liquid is excluded from on the substrate W by replacingHF present on the substrate W with a rinse liquid. In detail, thecontroller 3 opens the rinse liquid valve 46 while maintaining the firstguard facing state of the processing cup 8. As a result, the rinseliquid is discharged from the discharge port 19 a of the upper-surfacenozzle 19 toward the central part of the front surface Wa of thesubstrate W being in a rotational state. The rinse liquid supplied tothe front surface Wa of the substrate W moves to the peripheral edge ofthe substrate W while receiving a centrifugal force generated by therotation of the substrate W. Consequently, HF adhering to the surface ofthe substrate W is rinsed away by the rinse liquid.

The rinse liquid discharged from the peripheral edge of the substrate Wis discharged from the peripheral edge of the substrate W in the lateraldirection of the substrate W. The rinse liquid discharged from theperipheral edge of the substrate W is received by the inner wall of theinner guard 64, is then allowed to flow down along the inner wall of theinner guard 64, and is sent to the waste liquid treatment equipmentplaced outside the apparatus through the first cup 61 and through thedrainage pipe 76. When a predetermined period of time elapses from theopen of the rinse liquid valve 46, the controller 3 closes the rinseliquid valve 46. Consequently, the rinse step S4 is ended.

Thereafter, the controller 3 performs the SC1 step S5 (see FIG. 5) inwhich SC1 that is an example of an alkaline chemical liquid is suppliedto the front surface Wa of the substrate W. In detail, the controller 3opens the alkaline chemical-liquid valve 44. As a result, SC1 isdischarged from the discharge port 19 a of the upper-surface nozzle 19toward the central part of the front surface Wa of the substrate W beingin a rotational state. SC1 supplied to the front surface Wa of thesubstrate W moves to the peripheral edge of the substrate W whilereceiving a centrifugal force generated by the rotation of the substrateW. Consequently, the whole area of the front surface Wa of the substrateW is processed by use of SC1.

SC1 that has moved to the peripheral edge of the substrate W isdischarged from the peripheral edge of the substrate W in the lateraldirection of the substrate W. SC1 discharged from the peripheral edge ofthe substrate W is received by the inner wall of the inner guard 64, isthen allowed to flow down along the inner wall of the inner guard 64,and is sent to the waste liquid treatment equipment placed outside theapparatus through the first cup 61 and through the drainage pipe 76.

When a predetermined period of time elapses from the start of dischargeof SC1, the controller 3 closes the alkaline chemical-liquid valve 44,and stops the discharge of SC1 from the upper-surface nozzle 19.Consequently, the SC1 step S5 is ended.

Thereafter, the controller 3 performs the rinse step S6 (see FIG. 5) inwhich a chemical liquid is excluded from on the substrate W by replacingSC1 present on the substrate W with a rinse liquid. In detail, thecontroller 3 opens the rinse liquid valve 46 while maintaining the firstguard facing state of the processing cup 8. As a result, the rinseliquid is discharged from the discharge port 19 a of the upper-surfacenozzle 19 toward the central part of the front surface Wa of thesubstrate W being in a rotational state. The rinse liquid supplied tothe front surface Wa of the substrate W moves to the peripheral edge ofthe substrate W while receiving a centrifugal force generated by therotation of the substrate W. Consequently, SC1 adhering to the surfaceof the substrate W is rinsed away by the rinse liquid.

The rinse liquid discharged from the peripheral edge of the substrate Wis discharged from the peripheral edge of the substrate W in the lateraldirection of the substrate W. The rinse liquid discharged from theperipheral edge of the substrate W is received by the inner wall of theinner guard 64, is then allowed to flow down along the inner wall of theinner guard 64, and is sent to the waste liquid treatment equipmentplaced outside the apparatus through the first cup 61 and through thedrainage pipe 76. When a predetermined period of time elapses from theopen of the rinse liquid valve 46, the controller 3 closes the rinseliquid valve 46. Consequently, the rinse step S6 is ended.

Thereafter, the controller 3 performs the replacing step S7 (see FIG.5). The replacing step S7 is a step in which a rinse liquid on thesubstrate W is replaced by an organic solvent (in this example, IPA)that is lower in surface tension than the rinse liquid (water). Thecontroller 3 allows the outer guard 66 to face the peripheral endsurface of the substrate W (i.e., realizes a third guard facing state)by lowering the inner guard 64 and the intermediate guard 65 to thelower position while controlling the guard lifting unit 67.

Furthermore, the controller 3 opens the organic solvent valve 48. As aresult, IPA is discharged from the discharge port 19 a of theupper-surface nozzle 19 toward the central part of the front surface Waof the substrate W being in a rotational state. IPA supplied to thefront surface Wa of the substrate W receives a centrifugal forcegenerated by the rotation of the substrate W, and spreads over the wholearea of the front surface Wa of the substrate W. Consequently, in thewhole area of the front surface Wa of the substrate W, the rinse liquidadhering to the front surface Wa is replaced by an organic solvent. Theorganic solvent that moves on the front surface Wa of the substrate W isdischarged from the peripheral edge of the substrate W in the lateraldirection of the substrate W. The organic solvent discharged from theperipheral edge of the substrate W is received by the inner wall of theouter guard 66, is then allowed to flow down along the inner wall of theouter guard 66, and is sent to the collection equipment through thethird cup 63 and the collection pipe 78.

When a predetermined period of time elapses from the open of the organicsolvent valve 48, the controller 3 closes the organic solvent valve 48.Consequently, the replacing step S7 is ended.

Furthermore, after the end of the replacing step S7, the controller 3performs the sublimation drying step S8 (see FIG. 5). In the sublimationdrying step S8, a liquid sublimation agent is supplied to the frontsurface Wa of the substrate W, and a liquid film that is thick enough tosoak the pattern 100 is formed on the front surface Wa of the substrateW, and then a sublimation-agent film is formed by solidifying the liquidfilm. Thereafter, a sublimation agent included in the sublimation-agentfilm is sublimated by rotating the substrate W at a high speed. In thiscase, a liquid phase does not exist between the patterns 100 of thefront surface Wa of the substrate W when the substrate W is rotated at ahigh speed, and therefore it is possible to dry the substrate W whilelessening the problem of the pattern collapse. The sublimation dryingstep S8 will be described in detail as follows.

When a predetermined period of time elapses from the start of thehigh-speed rotation in the sublimation drying step S8, the controller 3stops the rotation of the spin chuck 5 while controlling the spin motor12 (S9 of FIG. 5: Stop of Rotation of Substrate W). Furthermore, thecontroller 3 lowers the outer guard 66 while controlling the guardlifting unit 67, and allows all guards to retreat downwardly from theperipheral end surface of the substrate W.

Thereafter, the substrate transfer robot CR enters the processing unit2, and carries an already-processed substrate W out of the processingunit 2 (S10 of FIG. 5: Carry-out of Substrate W). The substrate Wcarried out therefrom is delivered to the indexer robot IR from thesubstrate transfer robot CR, and is stored in the substrate container Cby means of the indexer robot IR.

FIG. 6 is a flowchart shown to describe the sublimation drying step S8of FIG. 5. FIG. 7A to FIG. 7D are schematic views, each showing a statearound the substrate W when the sublimation drying step S8 is performed.

The sublimation drying step S8 includes a sublimation-agent-liquid-filmplacing step T10 in which a liquid film (i.e., a sublimation-agentliquid film) 81 of a liquid sublimation agent is placed on the frontsurface Wa of the substrate W, a high vapor-pressure liquid supply stepin which a high vapor-pressure liquid that has vapor pressure higherthan water (vapor pressure higher than a sublimation agent) and thatdoes not include water is supplied to the rear surface Wb of thesubstrate W, and a vaporizing/cooling step T3 in which the supply of ahigh vapor-pressure liquid to the rear surface Wb is stopped after thesublimation-agent liquid film 81 is placed on the front surface Wa ofthe substrate W, and, as a result, vaporization heat is lost in responseto the vaporization of the high vapor-pressure liquid, and, as a result,a sublimation agent included in the sublimation-agent liquid film 81 iscooled. The sublimation agent included in the sublimation-agent liquidfilm 81 is solidified by performing the vaporizing/cooling step T3, anda solid sublimation-agent film 82 is formed on the front surface Wa ofthe substrate W. The sublimation drying step S8 also includes asublimating step T4 that sublimates the sublimation-agent film 82.

The sublimation-agent-liquid-film placing step T10 includes asublimation-agent supply step T1 in which a sublimation agent issupplied to the front surface Wa of the substrate W and a thinning stepT2 in which the sublimation agent supplied thereto is thinly spread (isthinned) on the front surface Wa of the substrate W by rotating thesubstrate W around the rotational axis A1 without supplying asublimation agent.

In the sublimation drying step S8, there is a fear that the sublimationof the sublimation agent will be obstructed if water is mixed with thesublimation-agent film 82 that has been solidified. Not only that, thereis another fear that the pattern collapse will be promoted by the factthat water is liquefied in the surface of the substrate W. Therefore,the sublimation drying step S8 is required to be performed in a state inwhich moisture has been excluded from the front surface Wa of thesubstrate W as much as possible so that water does not mix with thesublimation-agent liquid film 81 or does not mix with thesublimation-agent film 82 that has been solidified (i.e., whilemaintaining the front surface Wa of the substrate W at a low humidity).Therefore, the sublimation drying step S8 is performed in the shieldingspace 28 (see FIG. 7A and the like).

When the sublimation drying step S8 (sublimation-agent supply step T1)is started, the controller 3 lowers the shielding plate 17 from thenearby position to the shielding position while controlling theshielding-member lifting unit 27. Consequently, the shielding space 28is formed between the substrate-facing surface 20 a and the frontsurface Wa of the substrate W. Furthermore, the controller 3 lowers theinner guard 64 to the lower position while controlling the guard liftingunit 67, and, as a result, allows the intermediate guard 65 to face theperipheral end surface of the substrate W (i.e., realizes a second guardfacing state).

Thereafter, the controller 3 performs the sublimation-agent supply stepT1. In detail, the controller 3 opens the sublimation agent valve 33while keeping the rotation of the substrate W at the liquid treatmentspeed. As a result, a liquid sublimation agent is discharged from thedischarge port 19 a of the upper-surface nozzle 19 toward the centralpart of the front surface Wa of the substrate W being in a rotationalstate. The sublimation agent supplied to the front surface Wa of thesubstrate W receives a centrifugal force generated by the rotation ofthe substrate W, and moves to the peripheral edge of the substrate W.Consequently, a sublimation-agent liquid film 80 with which the wholearea of the front surface Wa of the substrate W is covered is formed asshown in FIG. 7A.

In the sublimation-agent supply step T1, the controller 3 supplies ahigh vapor-pressure liquid (high-temperature liquid) from the dischargeport 7 a of the lower-surface nozzle 7 toward the central part of therear surface Wb of the substrate W in parallel with the supply of asublimation agent to the front surface Wa of the substrate W. This highvapor-pressure liquid has a liquid temperature that is several degrees(° C.) higher than the freezing point of the sublimation agent suppliedto the front surface Wa of the substrate W. A high vapor-pressure liquidhaving such a liquid temperature is supplied to the rear surface Wb ofthe substrate W, and therefore it is possible to prevent immediatesolidification. Therefore, it is possible to form an excellentsublimation-agent liquid film on the front surface of the substrate.

Also, a high vapor-pressure liquid (i.e., IPA) is used as a liquid(high-temperature liquid) for the prevention of solidification asmentioned above, and therefore it is possible to warm a sublimationagent supplied to the front surface Wa of the substrate W while morereliably preventing water from mixing with the sublimation-agent liquidfilm 80 on the front surface Wa of the substrate W.

When such a period of time as to enable the sublimation-agent liquidfilm 80 to cover the whole area of the front surface Wa of the substrateW elapses, the controller 3 closes the sublimation agent valve 33.Consequently, the sublimation-agent supply step T1 is ended.

Thereafter, the controller 3 performs the thinning step T2. Thesubstrate W is rotated at a liquid treatment speed (about 300 rpm) whileclosing the sublimation agent valve 33 (i.e., in a state of stopping thesupply of the sublimation agent from the upper-surface nozzle 19). Inthe thinning step T2, it is possible to spread the sublimation agent bya centrifugal force generated by the rotation of the substrate W on thefront surface Wa of the substrate W. The thickness of thesublimation-agent liquid film 81 that has been thinned is, for example,about 10 μm. Consequently, it is possible to excellently form thesublimation-agent liquid film 81 that has an appropriate and smallthickness on the front surface Wa of the substrate W, and it is possibleto equalize the thickness of the sublimation-agent liquid film 81 in theplane of the substrate W.

Also, in the thinning step T2, the controller 3 supplies a highvapor-pressure liquid from the discharge port 7 a of the lower-surfacenozzle 7 toward the central part of the rear surface Wb of the substrateW. This high vapor-pressure liquid has a liquid temperature (T_(IPA))that is several degrees (° C.) higher than the freezing point (FP) ofthe sublimation agent supplied to the front surface Wa of the substrateW (T_(IPA)>FP). Therefore, the sublimation-agent liquid film 81 on thefront surface Wa of the substrate W is not immediately cooled to orbelow the freezing point of the sublimation agent by the supply of thehigh vapor-pressure liquid to the substrate W. The supply of a highvapor-pressure liquid to the rear surface Wb of the substrate W in thethinning step T2 continuously follows the supply of a highvapor-pressure liquid to the rear surface Wb of the substrate W in thesublimation-agent supply step T1.

The high vapor-pressure liquid is a solvent that does not include water,and therefore it is possible to allow the high vapor-pressure liquid tospread over the whole area of the rear surface Wb of the substrate Wwithout depending on whether the rear surface Wb of the substrate Wpresents hydrophobicity. Consequently, a liquid film 84 of a highvapor-pressure liquid with which the whole area of the rear surface Wbof the substrate W is covered is formed.

When a predetermined period of time elapses from the closing of thesublimation agent valve 33, the controller 3 closes the highvapor-pressure liquid valve 54. Consequently, the supply of a highvapor-pressure liquid to the rear surface Wb of the substrate W isstopped. Consequently, the thinning step T2 is ended.

Thereafter, the controller 3 performs the vaporizing/cooling step T3.The substrate W continues to rotate at the liquid treatment speed duringthe vaporizing/cooling step T3.

After the supply of the high vapor-pressure liquid to the rear surfaceWb of the substrate W is stopped, the vaporization of the highvapor-pressure liquid having a high vapor pressure is advanced in therear surface Wb of the substrate W. The heat of vaporization is lostfrom the rear surface Wb in response to the vaporization of the highvapor-pressure liquid in the rear surface Wb of the substrate W.Consequently, the substrate W is cooled, and the sublimation agentincluded in the sublimation-agent liquid film 81 formed on the frontsurface Wa of the substrate W is also cooled. In response to thecooling, the sublimation agent included in the sublimation-agent liquidfilm 81 is reduced in temperature to or below the freezing point (FP) ofthe sublimation agent (more specifically, lower in temperature than thefreezing point (FP)). Consequently, the sublimation agent included inthe sublimation-agent liquid film 81 is solidified. A solidsublimation-agent film 82 is formed on the front surface Wa of thesubstrate W by the fact that all of the sublimation agent included inthe sublimation-agent liquid film 81 is solidified. The temperature Tsof the sublimation-agent film 82 is lower than the freezing point(FP>Ts).

In the present preferred embodiment, the liquid film 84 of a highvapor-pressure liquid with which the whole area of the rear surface Wbof the substrate W is covered is formed in the thinning step T2.Therefore, the high vapor-pressure liquid is vaporized in the whole areaof the substrate W in the vaporizing/cooling step T3, andvaporizing/cooling is performed in the whole area of the substrate W,and therefore the sublimation agent is evenly cooled in the plane of thesubstrate W.

When a predetermined period of time elapses from the closing of the highvapor-pressure liquid valve 54, the vaporizing/cooling step T3 is ended.

Thereafter, the controller 3 performs the sublimating step T4. Thecontroller 3 lowers the intermediate guard 65 to the lower positionwhile controlling the guard lifting unit 67, and, as a result, allowsthe outer guard 66 to face the peripheral end surface of the substrate W(i.e., realizes a third guard facing state). Furthermore, the controller3 accelerates the rotation of the substrate W to a high speed (e.g.,about 1500 rpm) (rotational speed higher than in thesublimation-agent-liquid-film placing step T10 and in thevaporizing/cooling step T3). Furthermore, the controller 3 allows theshielding plate 17 to rotate at a speed equal to that of the rotation ofthe substrate W and in the same direction as the rotation of thesubstrate W while controlling the shielding-plate rotation unit 26. Thecontact speed between the sublimation-agent film 82 and itscircumambient atmosphere is increased in response to the high-speedrotation of the substrate W. This makes it possible to advance thesublimation of the sublimation-agent film 82, and hence makes itpossible to sublimate the sublimation-agent film in a short time.

Furthermore, the controller 3 opens the gas valve 50 in the sublimatingstep T4. As a result, a dehumidified gas is discharged from thedischarge port 19 a of the upper-surface nozzle 19 toward the centralpart of the front surface Wa of the substrate W being in a rotationalstate. This makes it possible to perform the sublimating step T4 whilekeeping the shielding space 28 in a low humidity state.

In the sublimating step T4, sublimating heat is lost in response to thesublimation of the sublimation-agent film 82, and the sublimation-agentfilm 82 is kept at or below the freezing point (melting point).Therefore, it is possible to prevent the sublimation agent included inthe sublimation-agent film 82 from being melted. This makes it possibleto excellently realize sublimation drying.

As described above, according to the present preferred embodiment, thesublimation-agent liquid film 81 is placed on the front surface Wa ofthe substrate W. Also, a high vapor-pressure liquid is supplied to therear surface Wb of the substrate W. After the sublimation-agent liquidfilm 81 is placed on the front surface Wa of the substrate W, the supplyof the high vapor-pressure liquid is stopped. Consequently, thesublimation agent included in the sublimation-agent liquid film iscooled by the fact that the heat of vaporization is lost from thesubstrate W in response to the vaporization of the high vapor-pressureliquid, and the sublimation-agent liquid film 81 is solidified. Thismakes it possible to excellently form the solid sublimation-agent film82 while preventing contamination of water into the solidsublimation-agent film 82.

Also, in the sublimating step T4, sublimating heat is lost in responseto the sublimation of the sublimation-agent film 82, and thesublimation-agent film 82 is kept at or below the freezing point(melting point). Therefore, it is possible to prevent the sublimationagent included in the sublimation-agent film 82 from being melted. Thismakes it possible to excellently realize sublimation drying.

Also, the high vapor-pressure liquid does not include water, andtherefore it is possible to supply the high vapor-pressure liquid to thewhole area of the rear surface Wb of the substrate W without dependingon whether the rear surface Wb of the substrate W presentshydrophobicity. This makes it possible to perform vaporizing and coolingin the whole area of the substrate W, and hence makes it possible toevenly cool the sublimation agent in the plane of the substrate W. Thismakes it possible to excellently solidify the sublimation agent includedin the sublimation-agent liquid film 81.

Also, a high vapor-pressure liquid supplied to the rear surface Wb ofthe substrate W has a liquid temperature higher than the freezing pointof a sublimation agent. Therefore, the sublimation agent on the frontsurface Wa of the substrate W is not immediately cooled to or below thefreezing point of the sublimation agent by the supply of the highvapor-pressure liquid to the substrate W. Therefore, it is also possibleto perform the disposition of a sublimation-agent liquid film on thefront surface Wa of the substrate W and the supply of a highvapor-pressure liquid to the substrate W in parallel with each other,and this also makes it possible to shorten the period of time of theentire processing.

FIG. 8A is a schematic view shown to describe a sublimation-agent supplystep according to a second substrate processing example.

A point of difference in which the second substrate processing examplediffers from the first substrate processing example is that water, not ahigh vapor-pressure liquid (IPA), is supplied to the rear surface Wb ofthe substrate W in parallel with the sublimation-agent supply step T1.

As shown by the broken line in FIG. 2, the processing unit 2 may alsoinclude a water supply unit 151 that supplies water to the rear surfaceWb of the substrate W (i.e., to a lower surface of the substrate W) heldby the spin chuck 5. The water supply unit 151 includes thelower-surface nozzle 7, the lower-surface supply pipe 52, a water pipe152 connected to the lower-surface supply pipe 52, and a water valve 153interposed in the water pipe 152. A water supply source is supplied tothe water pipe 152. DIW (deionized water) can be mentioned as thiswater, and yet carbonated water, electrolyzed ion water, hydrogen water,ozone water, hydrochloric acid water having a diluted concentration(e.g., about 10 to 100 ppm), restoration water (hydrogen water), ammoniawater, degassed water, etc., may be used.

Water is supplied to the rear surface Wb of the substrate W by openingthe water valve 153. The supply of water is continuously performed untilthe end of the sublimation-agent supply step T1, and is stopped at atiming at which the thinning step is started (i.e., at a timing at whichthe supply of a sublimation agent to the front surface of the substrateW is stopped).

According to the second substrate processing example, water is used as aliquid (high-temperature liquid) for the prevention of solidification,and therefore it is possible to make costs lower than in a case in whicha high vapor-pressure liquid is used as a high-temperature liquid.

Although one preferred embodiment of the present invention has beendescribed as above, the present invention can also be embodied in othermodes.

For example, the supply of a liquid (high-temperature liquid) for theprevention of solidification to the rear surface Wb, which is performedin parallel with the sublimation-agent supply step T1, may be startedbefore starting the sublimation-agent supply step T1. Also, it ispermissible not to supply a liquid (high-temperature liquid) for theprevention of solidification to the rear surface Wb of the substrate Win parallel with the sublimation-agent supply step T1 as in a thirdsubstrate processing example of FIG. 8B.

Also, it is also possible to exclude the thinning step T2. In this case,a high vapor-pressure liquid may be supplied to the rear surface Wb ofthe substrate W in parallel with the sublimation-agent supply step T1,and the supply of the high vapor-pressure liquid to the rear surface Wbof the substrate W may be stopped immediately after the end of thesublimation-agent supply step T1 (i.e., the vaporizing/cooling step T3may be started immediately).

Also, although a sublimation agent is supplied by the upper-surfacenozzle 19 that passes through the shielding plate 17 upwardly anddownwardly as described in the above preferred embodiment, thesublimation agent can be supplied by another nozzle. In this case, it isalso possible to supply a sublimation agent by use of a gas dischargenozzle 201 capable of radially discharging a gas in the lateraldirection as shown in FIG. 9.

The gas discharge nozzle 201 has a cylindrical nozzle body 204 having aflange portion 203 at its lower end. A gas discharge port 205 and a gasdischarge port 206 are outwardly bored in an outer peripheral surface,which is a side surface of the flange portion 203, in annular forms,respectively. A center gas-discharge port 207 is disposed at a lowersurface of the nozzle body 204. Therefore, a three-layer radial airflowmade by combining together a radial airflow formed by an inert gasdischarged from the center gas-discharge port 207 and a two-layer radialairflow discharged from the gas discharge ports 205 and 206 is formedabove the substrate W.

A liquid nozzle 208 is inserted in the nozzle body 204 upwardly anddownwardly. A discharge port 209 formed at a lower end of the liquidnozzle 208 faces a space below the nozzle body 204. A liquid sublimationagent is supplied to the liquid nozzle 208, and, accordingly, thesublimation agent is discharged downwardly from the discharge port 209.Likewise, in this case, it is possible to supply the sublimation agentto the front surface Wa of the substrate W while removing moisture fromthe front surface Wa of the substrate W.

Also, although the substrate processing apparatus 1 is an apparatus thatprocesses a substrate W of a semiconductor wafer as described in theaforementioned preferred embodiment, the substrate processing apparatusmay be an apparatus that processes substrates, such as substrates forliquid crystal displays, substrates for FPDs (Flat Panel Displays) suchas organic EL (electroluminescence) displays, substrates for opticaldisks, substrates for magnetic disks, substrates for magneto-opticaldisks, substrates for photomasks, ceramic substrates, and substrates forsolar cells.

Although the preferred embodiments of the present invention have beendescribed in detail, these preferred embodiments are merely concreteexamples used to clarify the technical contents of the presentinvention, and the present invention should not be understood by beinglimited to these concrete examples, and the scope of the presentinvention is limited solely by the appended claims.

This application corresponds to Japanese Patent Application No.2017-167866 filed in the Japan Patent Office on Aug. 31, 2017, and theentire disclosure of the application is incorporated herein byreference.

What is claimed is:
 1. A substrate drying method for drying a frontsurface of a substrate having a pattern, the substrate drying methodcomprising: a sublimation-agent-liquid-film placing step of placing aliquid film of a liquid sublimation agent on the front surface of thesubstrate; a high vapor-pressure liquid supply step of supplying a highvapor-pressure liquid that has vapor pressure higher than thesublimation agent to a rear surface that is a surface on a side oppositeto the front surface in the substrate; a vaporizing/cooling step of,after the liquid film of the sublimation agent is placed on the frontsurface of the substrate, stopping supplying the high vapor-pressureliquid, and, as a result, losing vaporization heat in response tovaporization of the high vapor-pressure liquid, and, as a result,cooling the sublimation agent, and, as a result, solidifying the liquidfilm of the sublimation agent, and, as a result, forming asublimation-agent film on the front surface of the substrate; and asublimating step of sublimating the sublimation-agent film.
 2. Thesubstrate drying method according to claim 1, wherein the highvapor-pressure liquid supplied to the rear surface of the substrate hasa liquid temperature higher than a freezing point of a sublimationagent.
 3. The substrate drying method according to claim 1, wherein thesublimation-agent-liquid-film placing step comprises: asublimation-agent supply step of supplying a sublimation agent to thefront surface of the substrate; and a thinning step of, on the frontsurface of the substrate, thinning the sublimation agent supplied to thefront surface of the substrate by rotating the substrate around apredetermined rotational axis without supplying a sublimation agent. 4.The substrate drying method according to claim 3, wherein the highvapor-pressure liquid supply step is performed in parallel with thethinning step.
 5. The substrate drying method according to claim 1,further comprising a high-temperature liquid supply step of supplying ahigh-temperature liquid having a liquid temperature higher than afreezing point of a sublimation agent to the rear surface of thesubstrate in parallel with the sublimation-agent-liquid-film placingstep.
 6. The substrate drying method according to claim 5, wherein thehigh-temperature liquid includes the high vapor-pressure liquid.
 7. Thesubstrate drying method according to claim 5, wherein thehigh-temperature liquid includes water.
 8. The substrate drying methodaccording to claim 1, further comprising: a substrate rotating step ofrotating the substrate around a predetermined rotational axis inparallel with at least either one of the sublimation-agent-liquid-filmplacing step and the vaporizing/cooling step; and a high-speed rotationstep of rotating the substrate around the predetermined rotational axisat a speed higher than in the substrate rotating step in parallel withthe sublimating step.